National Guard Engineering Education
General Levee Information • Levees are the most widely used method of flood control • The most extensive levee systems in the US are along the Mississippi and Sacramento rivers and their tributaries. • The first levees were about 3 ft high but now they average 24 feet with some areas as high as 50 feet
Types of Primary Levees • Earthen Levee: • Built out of soil or other natural material • Least expensive to build • Base must be large to provide the support required to withstand a heavy water surge • Not ideal in the absence of large amounts of land
I Wall Levee • A vertical wall partially embedded in the levee crown, or the tapered top • Not recommended when the soil is soft because the stability is reliant on the resistance from the soil • For stability reasons, I walls rarely exceed 7 feet above the ground’s surface
T wall levee • Has a horizontal base that reinforces the soil underneath the levee, making it one of the stronger types of levees • Requires piles be driven deeply into the ground • This makes T walls expensive to build • Typically used when walls higher than 7 feet are required
Double Wall Levee • Relatively new • Consists of 2 metal sheet pilings and filler made with sand and concrete • Most effective if there is a direct hit by a large item such as a barge because the filler will absorb some of the hit, preventing the levee from breaking
Secondary Levees: Sandbags • Made of burlap or other material that are filled with sand, soil or clay] • Inexpensive, can be transported empty and filled with local sand • In large flooding, water will seep through the bags and finer materials, such as clay, can leak out • Only dry sandbags can be stored for future use – wet sandbags become contaminated • Requires a lot of labor
Secondary Levees: Aqua Fences • Plywood panels are unfolded and secured with aluminum poles and connected to one another with PVC • Can be quickly and easily installed and dismantled and stored for future use • Large initial purchase is required; cannot be used in an unexpected emergency situation unless already acquired • Best for long-term emergency for areas of repeated flooding www.youtube.com/watch?v=lExOgQ73Fd4 http://www.youtube.com/watch?v=lExOgQ73Fd4
Secondary Levees: HESCO barriers • Collapsible wire mesh linked open top containers with a heavy-duty fabric liner, filled with sand, dirt or gravel • Can be quickly and easily set up, harder for water to seep through because of thickness • Must have room for the equipment required to fill the barriers; once in place, it cannot moved or stored for future use • Fabric has a lifespan of 3-4 years www.youtube.com/watch?v=mADScNThzso
Secondary Levees: DefenCell • Similar to HESCO barrier, but does not require the wire mesh • Can be quickly and easily set up, easily transportable, can be carried by a person or pushed off vehicle with no risk of damage • Harder for water to seep through because of thickness • Once in place, it cannot be moved DefenCell
How many sandbags and tons of sand?
On average, 250-500 sandbags are required to protect a single home that is being threatened by rising waters. To answer the following questions, use 425 as the number of sandbags required to protect a single home from rising waters.There are 65 homes in a threatened area. How many sandbags are required to protect these homes from rising waters? 65 homes x 425 bags per home = 27,625 bags
There are a group of buildings alongside a levee that is 15,840 ft. In order to protect these buildings from rising waters, determine the number of sandbags required to build a 2 ft. high secondary levee. 156,840 x 20 = 316,800
If 1 ton of sand can fill 50 sandbags, how many tons of sand are required to protect the single family homes and groups of buildings above from rising waters? 27,625(homes) + 316,800(buildings) = 344,425 bags 344,425/50 = 6888.5 tons of sand
Fargo flooding 2009
